Ultrasonic guided wave imaging of rail defects based on adaptive beamforming

Rails are a key component of railway infrastructure and their condition is crucial to the safe operation of trains. Ultrasonic guided wave technology is a method for long-distance detection and monitoring of rails. However, the complex structure of rails and the dispersion phenomenon of ultrasonic guided waves can lead to mode mixing, making it difficult to extract defect scattering signals and thus affecting the accuracy of defect detection. Therefore, this paper proposes an ultrasonic guided wave imaging method based on adaptive beamforming to improve the imaging accuracy of rail defects. Firstly, the guided wave signal is focused based on time reversal (TR). Then, according to the deviation between the reversed focused signal and the original excitation signal, the damage index (DI) for each propagation path is calculated. Finally, these indices are used as weighting vectors to perform adaptive weighting on the full matrix capture (FMC) signals for imaging. This method can narrow the main lobe width (MLW) and reduce the side lobe peak, thereby simultaneously enhancing the image contrast and resolution. Simulation and experimental results show that the proposed method can effectively suppress guided wave dispersion, increase the defect echo amplitude and significantly improve the imaging quality of rail defects. Compared with traditional total focusing method (TFM) imaging, the proposed method has significant improvements in the defect location, defect size and signal-to-noise ratio (SNR).